In recent years, electric vehicles and hybrid vehicles are beginning to prevail, which include devices such as motors and batteries, and which travel by driving the motors with power stored in the batteries. The electric vehicles charge their batteries with power supplied from external power supply devices. As for the hybrid vehicles, plug-in hybrid vehicles have been practically used, which allow their batteries to be charged by external power supply devices. The external power supply devices are power supply devices installed in ordinary houses or facilities such as commercial charging stations. When a power supply device supplies power to a vehicle, a plug at an end of a charging cable connected to the power supply device is connected to a power supply port which is provided in the vehicle as a power receiving connector. Then, power is supplied from the power supply device to the vehicle via a power supply line contained in the charging cable, and thereby the battery is charged.
Not only the power supply line but also other lines such as a grounding line, a control line, and the like are contained in the charging cable. The control line is a line used for transmission of a control signal such as a control pilot signal or the like used for power supply control to the power storage device. By transmitting and receiving the control signal between the power supply device and the vehicle via the control line, various states are detected such as the connection state of the charging cable, whether charging is possible or not, the state of charging, and the like, and charging control is performed according to the detected states.
Further, for practical use of vehicles that need external power supply, such as electric vehicles and hybrid vehicles, a communication function is required, which allows a vehicle and a power supply device to transmit and receive information for charging control, and communication information for management of the amount of charge, accounting, or the like.
Thus, standardization of communication such as power line communication has been progressed, in which a communication signal is superposed on a power supply line as a medium to allow communication between a vehicle and a power supply device. Further, the method of transmitting/receiving a communication signal is not limited to the power line communication, and standardization of communication such as inband communication has also been progressed, in which a communication signal is superposed on a control signal using a control line as a medium so as to be transmitted and received between a vehicle and a power supply device (refer to Non-Patent Literature 1, for example).
In the communications such as the power line communication and the inband communication, a superposition/separation unit using a transformer having a first coil and a second coil is connected to lines such as a power supply line, a grounding line, a control line, and the like. The superposition/separation unit superposes, on the above lines, a communication signal which is input or output to or from a communication device connected thereto via a communication line, and separates a communication signal from the above lines, whereby a vehicle and a power supply device are allowed to communicate with each other.
The vehicle and the power supply device each includes, for the power line communication or the inband communication, a communication device connected to a pair of power supply lines or to a grounding line and a control line, via a pair of communication lines. Such a communication device is required to have resistance to common mode noise that enters the communication device via the pair of communication lines as differential signal lines. In order to increase the resistance to the common mode noise, for example, a method has been implemented, in which a common mode choke coil for attenuating the common mode noise is interposed in the communication line.